Hydraulic timing device



P 1962 E. A. SCHWANDES ETAL 3,052,779

HYDRAULIC TIMING DEVICE 3 Sheets-Sheet 1 Filed Feb. 12, 1959 INVENTORS. E'Zmer' f2. Sc/zwzndes famunz J 5tmmaa/sk Sept. 4, 1962 Filed Feb. 12, 1959 E. A. SCHWANDES ETAL HYDRAULIC TIMING DEVICE Log. 7Z'me 5 Sheets-Sheet 3 L05. Current Lay. Current INVENTORS.

5277257 (/91 5chwznde6 Edmund J. Stramowskd vfttorweyr United States Patent Ofifice 3,052,779 Patented Sept. 4, 1962 3,052,779 HYDRAULIC TIMING DEVICE Elmer A. Schwandes and Edmund J. Strarnowski, Milwaukee, Wis., assignors to McGraw-Edison Electric Company, Milwaukee, Wis., a corporation of Delaware Filed Feb. 12, 1959, Ser. No. 792,773 13 Claims. (Cl. 200-97) This invention relates to hydraulic timing devices and more particularly to an adjustable hydraulic timing device for circuit interrupters and the like.

The time delay device forming the subject of the instant application is an improvement in the time delay device illustrated in detail in Patent 2,835,763 to A. Van Ryan et al. for a Repeating Polyphase Circuit Interrupter and assigned to the same assignee as the instant application.

Repeating circuit interrupters or reclosers of the type illustrated in the above cited patent are generally utilized in electric distribution systems in conjunction with other protective devices, such as fuses, wherein the repeating circuit interrupter is connected in series with the main line and located adjacent the source of power and the fuses are disposed in feeder lines radiating from the main line. Upon the occurrence of a fault, such circuit interrupters are designed to execute a successive series of circuit opening and closing operations which terminate in lockout or an open condition. The first group of this series of operations is usually rapid, that is, the main contacts of the interrupter open almost instantaneously following the initiation of fault current. Because most faults are temporary in nature, and clear after one or two rapid operations of the recloser, it is desirable that the branch fuses remain undamaged during the fast opening operations so that service in the branch circuits will be reestablished after normal conditions are restored. Accordingly, the opening time for this first group of operations is chosen to be more rapid than the time required for the fusible elements to melt. If the fault has not cleared after the series of fast operations, it is considered permanent and it is then desirable to isolate the feeder lines and perhaps the main line itself, depending on the location of the fault. The group of fast operations is, therefore, followed by a second group of operations in which the opening of the contacts is time delayed relative to the first group so that during the initial one of these delayed operations, the fuses carry the fault current for a period sufficient to result in melting of the fusible elements, and as a result, the feeder lines are isolated. The main contacts then open and again reclose. If the fault exists in one of the feeder lines, it is thereby isolated, and the circuit interrupter remains closed after the subsequent reclosing operation so that the main line remains energized. On the other hand, if the fault exists in the main line, the device again opens after a time delay and is locked open until manually reset.

Time delay for such delayed operations is accomplished by means of a time delay device which remains inactive during rapid operations and which is made active to retard opening during the time delayed operations.

The time delay device disclosed in the above identified patent had predetermined time current characteristics for its fast and slow opening operations. Because the rapid opening operations must be more rapid than the time required to melt the fuse, while the delayed operations must be sufiiciently slow to insure melting of the fuse, it can be seen that the time-current melting characteristic of the fuse must lie somewhere between the time-current characteristics of the circuit interrupter for fast and slow operations. This coordination of repeating circuit interrupters or reclosers and other protective devices such as fuses, is very difficult, however, because different varieties and types of such devices have various time-current characteristics which may not parallel those of the circuit interrupter. It can thus be seen that it is highly desirable to provide a circuit interrupter with means for quickly and accurately changing its time-current characteristic for delayed operations so as to facilitate its coordination with fuses and other types of protective devices.

It is an object of the invention to provide an improved hydraulic time delay device.

It is another object of the invention to provide a time delay device for controlling the opening of a circuit interrupter wherein the time-current characteristic of said circuit interrupter may be rapidly and accurately adjusted.

Another object of the invention is to provide a circuit interrupter having a time-current characteristic which may be selectively varied with respect to slope and amplitude.

It is a further object of the invention to provide a hy: draulic time delay device with means for adjusting it in a convenient step by step manner through a predetermined range of time delay values.

It is yet another object of the invention to provide a time delay device for circuit interrupters which facilitates their coordination with other protective devices.

It is a still further object of the invention to provide an encased hydraulic time delay device for circuit interrupters wherein the slope and the position of the time-current characteristic of the device may be easily and conveniently modified from the exterior of the casing. I

Other objects and advantages of the present invention will become apparent from the following detailed description taken in view of the drawings in which:

FIG. 1 is a front elevational view, partlyin section, of the time delay device according to the invention shown in conjunction with parts of a repeating circuit interrupter;-

FIG. 2 shows a typical time-current characteristic for repeating circuit interrupters and fuses;

FIG. 3 is a side elevational view, partly in section of the time delay device according to the invention;

FIG. 4 is a view taken along lines 4-4 of FIG..3; FIG. 5 is a view taken along lines 5-5 of FIG. 1; FIG. 6 is an elevational view of the time delay device according to the invention; FIG. 7 is a partial elevational view of the time delay device according to the invention showing means for ad-.

justing the time-current characteristic; and

FIGS. 8-10 show the various time-current characteristics possible in a repeating circuit interrupter incorporatments include a current responsive trip coil 15 which is connected in series with main interrupter contacts not shown, of the repeating circuit interrupter. When coil 15 is traversed by excessive current, it attracts magnetic plunger 16 downward and exerts a similar thrust upon an insulating link 17. Link 17 is pivotally connected to a rocking lever 18 which is fixedly pinned to a shaft 19, journaled on chassis 13. A hook shaped time delay latch finger 20 is pivotally attached to the free end of rocking lever 18 and extends generally upwardly. Latch finger 20 is biased clockwise with respect to rocking lever 18 by means of a torsion spring 22. Clockwise rotation of latch finger 20 is normally opposed by a cross pin 23 lying in the swinging i a-th of finger 20 and carried by a lever 24 which is pivoted about a fixedly positioned axis or pin 25. lever 24 is one of several that support a time delay device control bar 26.

In order to render the time delay device eifective to delay tripping by retarding downward movement of magnetic plunger 16, latch finger 20 must be allowed to engage a pin 27 extending transversely through the time delay arm 28. As long as the time delay control bar 26 remains in the position in which it is shown in FIG. 1, the biasing influence of torsion spring 22 is overcome and latch finger hook end 20 is free to move downwardly without engaging pin 27 and the time delay arm 28. Thus, in the first series of operations, magnetic plunger '16 may descend without retardation because time delay arm 28 is disconnected from latch finger 20. When plunger 16 descends during the flow of fault current in coil 15, rocking lever 18 and shaft 19 are rotated through a clockwise angle. Such rotation causes similar action on the part of a trip finger 29 shown in hidden lines in FIG. 1 and which is pinned to the end of shaft 19 behind a fragmentary part of the interrupter chassis 13. When coil is adequately energized, finger 29 rotates clockwise through a limited angle and trips the interrupter mechanism (not shown). Upon this event, the interrupter opens its main contacts in series with coil 15 and thereby de-energizes the coil and allows magnetic plunger 16 :to be retracted upwardly under the influence of a return spring 31 which is connected at its lower end to insulating link 17 and anchored at the upper end to cover plate 37.

In order to retard tripping of the interrupter, the influence of the time delay device 10 is brought into effect. This is accomplished through automatic means, not shown, associated with the interrupter for shifting the time delay control bar 26 to the right after the interrupter has executed a predetermined number of rapid opening operations in the manner just described. When the control bar 26 moves to the right, it carries with it finger retaining cross pin 23 thereby allowing the hook end of latch finger 20 to engage the pin 27 of time delay arm 28. Subsequent energization of series coil :15 will result in magnetic plunger 16 being drawn downwardly more slowly because of the hydraulic resistance created within the time delay device and which is transmitted to the time delay arm by means of an actuating rod extending into the time delay device 10.

It will be appreciated that the time required for the repeat-mg circuit interrupter contacts to open is governed by the rate of descent of magnetic plunger 16 into trip coil 15, and that this rate of descent is governed by the force of the solenoid minus the force necessary to trip the recloser and to overcome the effects of the time delay device 10. Hence, because the maximum uniform pull of the solenoid is a function of current in the solenoid coil, the opening time of the interrupter is a function of the fault current. Typical time-current characteristics of a repeating circuit interrupter are shown in FIG. 2 in which curve A represents fast opening operations and curve B represents operations wherein time delay device 10 is utilized.

Time delay device 10 includes a housing 35 sealed at its top by a gasketed cover plate 37 to define a chamber 36. A seal assembly 38 is disposed in cover plate 37 to permit actuating rod 30 to extend therethrough, without allowing the escape of the hydraulic fluid 39 which substantially fills chamber 36.

Downward thrust on actuating rod 30 is resisted by a reciprocating piston 40 which tends to expell the hydraulic fluid 39 from dash-pot cylinder 40'. The piston 40 is normally biased upwardly by a helical spring 41 disposed within cylinder 40' below piston 40 and the rate of descent of said piston at high values of fault current is governed by a first needle valve assembly 43 and its rate of descent at low fault current values is controlled by a second needle valve assembly (shown in FIG. 3) both of which will be described in greater detail hereinafter. A valve plate 42 is reciprocably mounted on the lower end of piston 40 by a plurality of tab members 42 so that during the upward stroke of piston 40, valve plate 42 is forced away from said lower end, as shown in FIG. 1, whereby hydraulic fluid may be drawn in under piston 40 through orifices 60, aperture 61, and around valve plate 42. When piston 40 descends the hydraulic fluid 39 forces valve plate 42 against the lower end of piston 40 thereby blocking aperture 61 and preventing the escape of fluid therethrough.

The needle valve assembly 43 includes a cylindrical member 44 which is threadably secured within the chamber 36 and is provided with an axial bore 45 for slidably receiving biasing spring adjusting sleeve 46. Adjusting sleeve 46 is in turn provided with a head portion 47 having a frusto-conical surface 43 formed thereon. Member 44 is also provided with an opening 50 at its lower end which defines a seat for a needle valve 52 extending through it. A coil spring 53 is disposed between the upper end of needle valve 52 and the under side of adjusting sleeve 46 so that needle valve 52 is biased toward opening 50. Communication between opening 50 and cylinder 40' is established by means of a groove 54 formed in one side of the lower end of cylinder 40' and which opens into a cavity 54 formed below opening 50 and in communication therewith. Upon a rapid descent of piston 40, hydraulic fluid 39 in cylinder 40' forces needle valve 52 away from opening 50 against the biasing force of spring 53 and flows into bore 45. An axial bore 64 is provided in adjusting sleeve 46 for loosely receiving a valve positioning guide pin 63 on needle valve 52 while allowing the hydraulic fluid in bore 45 to discharge to the upper end of chamber 36 as hydraulic piston 40 descends. In order to facilitate the flow of fluid past valve positioning guide pin 63, a pair of flats are machined on either side of biasing spring adjusting sleeve 46 to provide a pair of rectangular openings 64'.

Referring now to FIGS. 3 and 4 the second needle valve assembly 100 comprises a valve member 101 adapted to control the flow of hydraulic fluid 39 through a passage 103 which also connects chamber 36 with groove 54 in cylinder 40'. The valve member 101 comprises a threaded body portion 105 and a co-axial valve portion 106 of reduced diameter. Body portion 105 is received within a threaded bore 108 whose axis is substantially perpendicu lar to that of passage 103 and substantially parallel to push rod 69. A second bore 110 of substantially reduced diameter relative to threaded bore 108, slidably receives valve portion 106 and extends co-axially from the inner end of threaded bore 108 to intersect passage 103. It can be seen from FIG. 3 that by suitably rotating valve member 101, valve portion 106 will be moved either laterally inwardly or outwardly of the passage 103, thereby varying the degree that passage 103 is restricted. A nut 112 may be provided to help secure valve member 101 in its operative position.

It can be seen, therefore, that upon the descent of piston 40, the hydraulic fluid from cylinder 40 can either exhaust through opening 50, past valve 52 and through passage 64 or past valve portion 106 and through passage 103. If the rate of descent of this piston is sufliciently slow, passage 103 will be able to accommodate all of the fluid displaced from cylinder and as a result, the pressure below valve 52 will not be sufficient to overcome the biasing force ofspring 53 so that valve 52 remains in its closed position and all of this fluid exhausts past needle 106 and through passage 103. On the other hand, if piston 40 descends rapidly upon the occurrence of a large fault current, the first needle valve assembly 43 will be operated to exhaust a major portion of the hydraulic fluid displaced by piston 40, because the capacity of passage 103 will be insufficient for this purpose.

Because hydraulic fluid 39 is substantially incompressible, the rate of discharge through opening and passage 103 governs the rate at which piston 40 can descend and, hence, the time delay characteristics of the device. This rate of discharge, of course, is governed by the biasing force of spring 53 and the position of valve portion 106 and as a result, the time delay characteristics of the device may be varied by modifying the flow restricting effect of these members.

With respect to biasing spring 53, this variation is accomplished, in the illustrated embodiment, by moving adjusting sleeve 46 axially in bore 45 to vary the compression of biasing spring 53. For this purpose, a spring pressure adjusting sleeve positioning assembly 65, as shown in FIGS. 5 and 6, is mounted on a base portion 35 integral with the front Wall of housing 35 and includes a push rod assembly 66 and a push rod positioning assembly 68.

Push rod assembly 66 includes a push rod 69 which is slidably received in a cylindrical bore 70 formed in base portion 35 and one end thereof passes through a suitably sealed aperture 72 in the wall of a time delay housing 35. As a result, push rod 69 may reciprocate through said wall while the escape of hydraulic fluid 39 from chamber 36 is prevented. The end of push rod 69 disposed within chamber 36 terminates in a conical surface 74 which engages the frustro-conical surface 48 of the upper end 47 of spring pressure adjusting sleeve 46. A helical spring 76 is disposed around the portion of push rod 69 disposed within bore 70 between its head 77 and the lower end of bore 70 so that said rod is thereby urged outwardly from the housing 35. Such outward movement is prevented, however, by a stop 78 projecting beyond the outer end of cylindrical bore 70 into the path of said push rod.

The push rod positioning assembly includes a turret plate 80 and a plurality of push rod positioning pins 82 extending through said plate and retained in position by nuts 83. Turret plate 80 is rotatably mounted on base 35 by means of a bolt 84 received through clearance hole 85 in turret plate 80 and threadably secured in tapped hole 86. The positioning of turret plate 80 against base 35' is achieved by means of a nut 87 threaded on bolt 84. Positioning pins 82 are threadably disposed in suitable tapped holes formed in turret plate 80 at equi-radial spaced apart locations near the periphery thereof and each of said pins extends through said turret plate a different predetermined distance. As shown in FIG. 5, tapped hole 86 is so located relative to bore that a circle joining the axes of positioning pins 82 will also contain the axis of push rod 69 so that upon rotation of turret plate 80 each of the positioning pins 82 Will be successively coaxial with said push rod.

In operation, when it is desired to change the" timecurrent characteristic of the device by modifying the biasing force of spring 53, nut 84 is loosened and turret plate 80 is rotated until the appropriate positioning pin 82 is co-axial with push rod 69 and nut 84 is again tightened until turret plate 80 encounters base portion 35. The positioning pin 82 will then engage the head 77 of push rod 69 and force it a distance into chamber 36 predetermined by the distance that the particular positioning pin extends through turret plate 80. As can be seen in FIG. 7, as push rod 69 is forced to the right from the full to the dotted position, its conical surface 74 acting against frustro-conical surface 48 will force spring pressure adjusting sleeve 46 downwardly compressing spring 53 and increasing the biasing force on needle valve 52. Conversely, movement of push rod 69 to the left allows adjusting sleeve 4-9 to rise thereby diminishing the biasing force of spring 53 on needle valve 52. It can be seen, therefore, that each of the positioning pins 82 will force push rod 69 a different distance into chamber 36 and result in a predetermined different biasing force to be placed upon needle valve 52 by spring 53.

Because the biasing force on needle valve 52 determines the rate at which the hydraulic fluid can be discharged from cylinder 40 past needle valve 52, it will also determine the rate of descent of hydraulic piston 40 for any given fault current and setting of 'valve member 101. Hence, it can be seen that each of the positions of push rod 69 predetermined for it by positioning pins 82 will result in a different predetermined time-current characteristic for the recloser. For example, assume that positioning pin 82C extends a first predetermined distance through turret plate and that each of the succeeding positioning pins 82D, 82E, 82F, 82G, and 82H extend a predetermined distance farther than the preceding positioning pin. Engagement of push rod 69 by successive positioning pins 82 will result in a succeedingly greater biasing force to be placed on valve 52 and thereby give the recloser a family of time-current characteristics similar to those shown in FIG. 8 in which curve A is the rapid opening curve and each of the other curves, C, D, E, F, G, and H represent the time-current characteristic which exists when the corresponding positioning pin 82 is in engagement with push rod 69.

It will be recalled that at very low values of fault current, the needle valve assembly 43 does not operate and as a result needle valve assembly governs the timecurrent characteristic at low current values. This ac counts for the divergence of the time-current characteristics C, D, E, F, G near the minimum trip current of the device I At relatively higher values of fault cur rent, however, passage 103 will not be sufficient to exhaust the discharge from cylinder 40 so that valve 52 will be moved away from its seat 50 in the manner above described. At such higher current values, the time delay of the device will be affected by the biasing force on' can be further modified by changing the position of valve portion 106 in passage 103 which will have the effect of vertically moving the low fault current end of all of' the time delay curves of FIG. 8.

The entire time delay curve can be moved vertically without changing its slope, if desired, by adjusting the second needle valve assembly 100 each time a different positioning pin 82 is utilized to give a family of characteristics similar to that shown in FIG. 9. Hence, if valve portion 106 is moved a predetermined greater distance into bore 110 each time an increased biasing force is placed on valve 52, both the high and low current ends of the time-current characteristics will be moved vertically as in FIG. 9 where each successive curve C, D, E,

F, G, and H is vertically displaced relative to its- This will give a family of acteristic of a circuit interrupter provided with a time delay device according to the invention can be conveniently and rapidly changed both as to slope and amplitude to facilitate its coordination with other protective devices.

Although only a single preferred embodiment of the invention has been described, it will be understood by those skilled in the art that it may take a number of different forms and be variously embodied without departing from the true spirit thereof. It is, therefore, to be construed according to the appended claims.

We claim:

1. A hydraulic time delay device having a housing, a cylinder disposed within said housing, a piston reciprocable in said cylinder, said cylinder having an aperture formed therein for discharging hydraulic fluid when said piston descends in said cylinder, valve means for controlling the rate of discharge of hydraulic fluid through said aperture, a member mounted in said housing and movable relative to said valve means, a biasing spring disposed between said valve means and said member and urging said valve in a flow restricting direction to retard the descent of said piston, push rod means extending through said housing and operatively engaging said member so that movement of said push rod means in a first direction forces said member to move in a spring compressing direction, and means for selectively moving said push rod in said first direction in predetermined increments so that said biasing spring may be adjusted through a predetermined range of biasing values whereby the time delay characteristics of said device may be varied through a predetermined range of values.

2. A hydraulic time delay device having a housing, a cylinder disposed within said housing, a piston reciprocable in said cylinder, said cylinder having an aperture formed therein for discharging hydraulic fluid when said piston descends in said cylinder, valve means for controlling the rate of discharge through said aperture, a member mounted substantially coaxially with said valve means and movable relative thereto, a biasing spring disposed between said valve means and said member and urging said valve means in a flow restricting direction to retard the descent of said piston, push rod means extending through said housing and operatively engaging said sleeve member so that movement of said push rod in a first direction forces said member toward said valve means to compress said spring, a push rod positioning member having a plurality of push rod engaging portions each disposed a different predetermined distance toward said push rod, said push rod positioning member being movable relative to said push rod so that said portions are selectively engageable with said push rod to move it in predetermined increments in said first direc tion so that said biasing spring may be adjusted through a predetermined range of biasing values whereby the time delay characteristics of said device may be varied through a predetermined range of values.

3. A hydraulic time delay device having a housing, a cylinder disposed within said housing, a piston reciprocable in said cylinder, said cylinder having an aperture formed therein for discharging hydraulic fluid when said piston descends in said cylinder, valve means for controlling the rate of discharge of hydraulic fluid through said aperture, biasing spring means urging said valve means in a discharge restricting direction, push rod means extending through said housing and operatively coupled to said spring means so that movement of said push rod in a first direction results in compression of said biasing spring against said valve means, a turret plate rotatably mounted on said housing, a plurality of push rod positioning portions disposed in spaced apart relation around the rotational axis of said turret plate and each extending a different predetermined distance toward said push rod and in a direction generally parallel to said rotational axis, each of said positioning portions being selectively engageable with said push rod upon rotation of said turret plate to force said push rod a different predetermined distance in said first direction so that said biasing spring may be adjusted through a range of biasing values in predetermined increments whereby the time delay characteristics of said device may be varied in a step by step manner through a predetermined range of values.

4. A hydraulic time delay device having a housing, a cylinder disposed within said housing, a piston reciprocable in said cylinder, said cylinder having an aperture formed therein for discharging hydraulic fluid when said piston descends, valve means in said aperture for controlling the rate of discharge from said cylinder, a member disposed in said housing and movable relative to said valve means, a biasing spring disposed between said valve and said member and urging said valve in a flow restricting direction relative to said aperture, push rod means extending through said housing and operatively engaging said member so that movement of said push rod in a first direction forces said member in a spring compressing direction, a turret plate rotatably mounted on said housin a plurality of push rod positioning portions disposed in spaced apart relation around the rotational axis of said turret plate and each extending generally parallel to said rotational axis a difierent predetermined distance .toward said push rod, each of said positioning portions being selectively engageable with said push rod upon rotation of said turret plate to force said push rod a different predetermined distance in said first direction so that said biasing spring may be adjusted through a predetermined range of biasing values whereby the time delay characteristics of said device may be varied through a predetermined range of values.

5. A hydraulic time delay device having a housing, a cylinder disposed within said housing, a piston rec-iprocable in said cylinder, said cylinder having an aperture formed therein for discharging hydraulic fluid when said piston descends, valve means in said aperture for controlling the rate of discharge of hydraulic fluid therethrough, a second cylinder connected at one end to said aperture and surrounding said valve means, a sleeve member slidably received within the other end of said second cylinder, a biasing spring disposed between said valve means and said sleeve member and urging said valve means toward said aperture, push rod means extending through said housing and operatively engaging said sleeve member so that movement of said push rod in a first direction forces said sleeve member into said second cylinder to compress said biasing spring, a turret plate rotatably mounted on said housing, a plurality of push rod positioning pins disposed in spaced apart relation around the periphery of said turret plate and each extending a different predetermined distance toward said push rod and in a direction substantially parallel to the rotational axis of said turret plate, each of said positioning pins being selectively engageable with said push rod upon rotation of said turrent plate to force said push rod a different predetermined distance in said first direction so that said biasing spring may be adjusted in a step by step manner through a predetermined range of biasing values whereby the time delay characteristics of said device may be varied in predetermined increments.

6. In a circuit interrupter having fault current sensing means and operating means actuatable by said fault current sensing means wherein the speed at which said operating means is actuated is a function of the magnitude of the fault current, the combination of time delay means for retarding the actuation of said operating means under the influence of said fault current sensing means, said time delay means including a first selectively variable means whose time delay characteristic is independent of the magnitude of said fault current for varying the operating time of said operating means at low current values, said time delay means also including a second selectively variable means whose time delay characteristic is dependent on the magnitude of said fault current for varying the operating time of said operating means at higher fault current values, whereby the amplitude and slope of the time current characteristic of said time delay means can be selectively varied.

7. In a repeating circuit interrupter responsive to fault currents, a hydraulic time delay device having a piston reciprocable in a cylinder, first and second valve means controlling the rate of discharge of hydraulic fluid from said cylinder, means for exerting a biasing force on said first valve means to urge it in a discharge restricting direction in opposition to the flow of said hydraulic fluid, means for adjusting said biasing force exerting means in a step by step manner through a predetermined range of biasing forces, and means for adjusting said second valve means in a flow restricting direction, whereby the time delay characteristics of the device may be selectively varied over a predetermined range of time delay values, the discharge through said first valve means being dependent on the magnitude of said fault current for controlling the time delay of said circuit interrupter at high fault current values, the flow restricting effect of said second valve means being independent of said fault current for controlling the time delay of said circuit interrupter at low fault current values.

8. In a circuit interrupter responsive to overload currents, a hydraulic time delay device having a housing, a cylinder disposed within said housing, a piston reciprocable in said cylinder, said cylinder having first and second apertures formed therein for discharging hydraulic fluid when said piston descends in said cylinder, first and second valve means for controlling of the rate of discharge of hydraulic fluid through said first and second apertures respectively, a member disposed in said housing and movable relative to said first valve means, a biasing spring disposed between said valve means and said member and urging said first valve means toward said aperture, means for selectively moving said member a plurality of predetermined distances in a spring compressing direction so that said biasing spring may be adjusted in a step by step manner through a predetermined range of biasing values, and means for varying the restricting effect of said second valve means in said second aperture, the flow restricting effect of said first valve means being dependent upon the magnitude of said fault current so that the time delay characteristic of said circuit interrupter may be controlled for high fault current values, the flow restricting effect of said second valve means being independent of the magnitude of said fault current for controlling the time delay characteristic of said circuit interrupter for low fault current values.

9. In combination, a circuit interrupter having electromagnetic fault current sensing means and operating means operable thereby, hydraulic time delay means for said fault current sensing means having a piston reciprocable in a cylinder, first and second valve means for controlling the rate of discharge of hydraulic fluid from said cylinder, the discharge through said first valve means being a function of the fault current in said sensing means, the discharge through said second valve means being independent of said fault current, said first and second valve means being adjustable so that the time delay characteristics of said circuit interrupter can be varied for all values of fault current.

10. A circuit interrupter having electromagnetic fault current sensing means, operating means actuable by said fault current sensing means, hydraulic time delay means for retarding the actuation of said operating means, said hydraulic time delay means including a piston reciprocable in a cylinder, first valve means controlling the rate of discharge of hydraulic fluid from said cylinder, means for exerting a biasing force on said valve means to urge it in a discharge restricting direction in opposition to the flow of said hydraulic fluid, so that the rate of discharge past said valve means is a function of the magnitude of said fault current, whereby the circuit interrupter will operate along an inverse time current characteristic, and means for adjusting said biasing force exerting the means in predetermined distinct and discontinuous increments through a range of biasing forces so that the time delay characteristic of said circuit interrupter can be varied for high fault current values, and second selectively adjustable valve means for controlling the rate of discharge of by draulic fluid from said cylinder, the flow restricting effect of said second valve means being independent of the magnitude of said fault current so that the time delay characteristic of said circuit interrupter may be controlled for low fault current values.

11. A circuit interrupter having electromagnetic fault current sensing means, operating means actuable by said fault current sensing means, hydraulic time delay means for retarding said electromagnetic fault current sensing means, said hydraulic time delay means including a piston reciprocable in a cylinder, a first discharge aperture in said cylinder, first valve means controlling the rate of discharge of hydraulic fluid through said aperture, biasing spring means engaging said first valve means to urge it toward said aperture in opposition to the flow of said hydraulic fluid, so that the discharge area of said aperture and the rate of discharge past said first valve means is a function of the magnitude of said fault current, whereby the circuit interrupter will operate along an inverse time current characteristic, and means for adjusting said biasing force exerting the means in predetermined distinct and discontinuous increments through a range of biasing forces so that the time delay characteristic of said circuit interrupter can be varied for high fault current values, and a second discharge aperture in said cylinder, second selectively variable valve means controlling the rate of discharge of hydraulic fluid through said second aperture, the flow restricting effect of said second valve means being inde pendent of the magnitude of said fault current so that the time delay characteristics of said circuit interrupter may be varied for low fault current values.

12. A circuit interrupter having fault current sensing means, operating means actuable in response to said fault current sensing means, and time delay means for delaying the actuation of said operating means in an inverse manner relative to the magnitude of said fault current, whereby said circuit interrupter will operate along an inverse time current characteristic, said time delay means including a first delay means whose time delay effect is independent of the magnitude of said fault current, said first delay means being selectively changeable in predetermined increments for varying the time delay of said operating means in the low current portion of said time current characteristic, said time delay means also including a second delay means whose time delay effect is dependent upon the magnitude of said fault current, said second delay means being selectively changeable in predetermined increments for varying the time delay of said operating means in the high current portion of said time current characteristic, whereby the operation of said circuit interrupter may be changed from one preselected time current characteristic to another.

13. A circuit interrupter having fault current sensing means, operating means actuable in response to said fault current sensing means, and time delay means for delaying the actuation of said operating means in an inverse manner relative to the magnitude of said fault current, whereby said circuit interrupter will operate along an inverse time current characteristic, said time delay means including first and second selectively changeable time delay modifying means so that a plurality of preselected time delay modifying values may be obtained, said first modifying means being independent of the magnitude of 1 '1 said fault current and thereby operative to modify the time delay of said operating means in the low current portion of said time current characteristic, said second modifying means being dependent on the magnitude of said fault current and thereby operative to modify the time delay of said operating means in the high current portion of said time current characteristic, the change of at least one of said first and second modifying means being operative to change the operation of said circuit References Cited in the file of this patent interrupter from one preselected time current charac- 10 2,902,088

teristic to another.

UNITED STATES PATENTS Cheney June 22, 1920 Wilhelm May 15, 1939 Rittenhouse June 10, 1941 Jensen Feb. 27, 1951 Ponstingel Feb. 24, 1953 Van Ryan et al Nov. 4, 1958 Griffes et a1 Sept. 1, 1959 

